Direct thermal imaging on paper is well known in the art. An image is formed by causing a chemical reaction on a specially coated paper that turns black when heated. In a typical direct thermal imaging process on paper, ceramic heating elements inside a print head, which are in contact with the paper, selectively turn on and off in a pattern, thereby forming the printed image (for example, alpha-numeric, bar codes, or graphics). It is also possible to produce an image in gray scale with a direct thermal imaging printer. In other words, the image is composed not only of black and white, but also gray, which provides a better reproduction of the image.
In a thermal transfer printer device, the recording paper is sandwiched under pressure along with an ink sheet between a platen roller and a thermal head. The ink sheet consists of a base film coated with a heat-sublimable dye, and is disposed such that the heat-sublimable dye is pressed against the recording paper. A plurality of heating elements are provided on one side of the thermal head, and when current is sent through the thermal head these heating elements generate heat according to the printed data, and heat the heat-sublimable dye via the base film. This results in the heat-sublimable dye being sublimated and transferred onto the recording sheet.